Biosensors for chemical and biological agents of defence interest

Microbial biosensor for direct determination of nitrophenyl-substituted organophosphate nerve agents using genetically engineered Moraxella sp

A microbial biosensor consisting of a dissolved oxygen electrode modified with the genetically engineered PNP-degrader Moraxella sp. displaying organophosphorus hydrolase (OPH) on the cell surface for sensitive, selective, rapid and direct determination of p-nitrophenyl (PNP)-substituted organophosphates (OPs) is reported. Surface-expressed OPH works in tandem with the PNP oxidation machinery of the Moraxella sp. to degrade PNP-substituted OPs and PNP simultaneously while consuming oxygen, that is proportional to the analyte concentration. The optimum performance was obtained by electrodes constructed using 0.35 mg dry weight of cell and operating at pH 7.5. Operating at optimum conditions the biosensor was able to measure as low as 0.1 microM (27.5 ppb) of paraoxon and had excellent selectivity against triazines, carbamates and OPs without PNP substitutent. The biosensor was stable for a week when stored at 4 degrees C. The applicability of the biosensor to measure OPs in lake water was demonstrated.

Carbon nanotube based aliphatic hydrocarbon sensor

A hybrid multi-walled carbon nanotube (MWCNT) based chemical sensor was designed and developed by integration of microfabrication techniques with nano-assembly. This integrated sensing mechanism on a chip, comprised of thiol functionalized MWCNTs that functioned as transducers which were integrated with micro-electrode array measurement sites. The detection of the four fundamental hydrocarbons belonging to the aliphatic hydrocarbon family--methanol, ethanol, propanol and butanol was experimentally demonstrated. High degree of selectivity was demonstrated by repeated robust identification of individual hydro carbons belonging to the same family. The sensor demonstrated 1 ppm detection sensitivity. The detection mechanism was based on nano-scale transduction of the detection of the localized binding event between the functional binding sites and the chemical species of interest. Specific electrical signatures for each of these chemicals were identified using multiple levels of data analysis comprising of Fast Fourier Transformation (FFT) and Power Spectral Density (PSD). The sensor demonstrated a rapid response time with portability, accuracy and versatility for the in situ detection of multiple chemical agents, with potential for automation.

Microelectrode array recordings of cardiac action potentials as a high throughput method to evaluate pesticide toxicity

The threat of environmental pollution, biological warfare agent dissemination and new diseases in recent decades has increased research into cell-based biosensors. The creation of this class of sensors could specifically aid the detection of toxic chemicals and their effects in the environment, such as pyrethroid pesticides. Pyrethroids are synthetic pesticides that have been used increasingly over the last decade to replace other pesticides like DDT. In this study we used a high-throughput method to detect pyrethroids by using multielectrode extracellular recordings from cardiac cells. The data from this cell-electrode hybrid system was compared to published results obtained with patch-clamp electrophysiology and also used as an alternative method to further understand pyrethroid effects. Our biosensor consisted of a confluent monolayer of cardiac myocytes cultured on microelectrode arrays (MEA) composed of 60 substrate-integrated electrodes. Spontaneous activity of these beating cells produced extracellular field potentials in the range of 100 microV to nearly 1200 microV with a beating frequency of 0.5-4 Hz. All of the tested pyrethroids; alpha-Cypermethrin, Tetramethrin and Tefluthrin, produced similar changes in the electrophysiological properties of the cardiac myocytes, namely reduced beating frequency and amplitude. The sensitivity of our toxin detection method was comparable to earlier patch-clamp studies, which indicates that, in specific applications, high-throughput extracellular methods can replace single-cell studies. Moreover, the similar effect of all three pyrethroids on the measured parameters suggests, that not only detection of the toxins but, their classification might also be possible with this method. Overall our results support the idea that whole cell biosensors might be viable alternatives when compared to current toxin detection methods.

Toxin detection based on action potential shape analysis using a realistic mathematical model of differentiated NG108-15 cells

The NG108-15 neuroblastoma/glioma hybrid cell line has been frequently used for toxin detection, pharmaceutical screening and as a whole-cell biosensor. However, detailed analysis of its action potentials during toxin or drug administration has not been accomplished previously using patch clamp electrophysiology. In order to explore the possibility of identifying toxins based on their effect on the shape of intracellularly or extracellularly detected action potentials, we created a computer model of the action potential generation of this cell type. To generate the experimental data to validate the model, voltage dependent sodium, potassium and high-threshold calcium currents, as well as action potentials, were recorded from NG108-15 cells with conventional whole-cell patch-clamp methods. Based on the classic Hodgkin-Huxley formalism and the linear thermodynamic description of the rate constants, ion-channel parameters were estimated using an automatic fitting method. Utilizing the established parameters, action potentials were generated in the model and were optimized to represent the actual recorded action potentials to establish baseline conditions. To demonstrate the applicability of the method for toxin detection and discrimination, the effect of tetrodotoxin (a sodium channel blocker) and tefluthrin (a pyrethroid that is a sodium channel opener) were studied. The two toxins affected the shape of the action potentials differently and their respective effects were identified based on the changes in the fitted parameters. Our results represent one of the first steps to establish a complex model of NG108-15 cells for quantitative toxin detection based on action potential shape analysis of the experimental results.

DNA-Directed Protein Immobilization for Simultaneous Detection of Multiple Analytes by Surface Plasmon Resonance Biosensor

A versatile multichannel biosensor surface is prepared by site-directed immobilization of single-stranded DNA-protein conjugates onto a patterned self-assembled monolayer composed of ssDNA thiols and oligo(ethylene glycol)-terminated thiols. The conjugates each consist of an antibody chemically linked to a unique ssDNA target with a sequence complementary to the surface-bound ssDNA probes and are immobilized on the surface via sequence-specific hybridization. The exceptional specificity of DNA hybridization combined with the diversity of available sequences makes this platform perfect for multichannel sensors. Once the surface is patterned with the appropriate probe sequences, sequence-specific hybridization sorts out the target conjugates and directs them to the appropriate spots on the surface. Previously (Boozer, C. L.; Ladd, J.; Chen, S.; Yu, Q.; Homola, J.; Jiang, S. Anal. Chem. 2004, 76, 6967-6972), we performed proof-of-concept experiments demonstrating the feasibililty of using DNA-directed protein immobilization to produce a single channel biosensor. In this work, we extend this technique and employ DNA-directed protein immobilization to functionalize a multichannel biosensor, which was used for the simultaneous detection of a set of three fertility hormones: human chorionic gonadotropin, human luteinizing hormone, and follicle stimulating hormone by surface plasmon resonance sensor.

Association of different prediction methods for determination of the efficiency and selectivity on neuron-based sensors

A technique has been developed to determine the efficiency and the selectivity of a single neuron-based sensor in identifying the nature of the chemical agents in an unknown sample. This has been achieved by exploiting the unique electrical identifiers, also known as "signature patterns", generated by the neuronal cell membrane. These were generated based on the variations to the extracellular electrical activity, due to the effect of a broad range of chemical agents. We demonstrate the prediction capability of the sensor in identifying the nature of an unknown test sample from a combination of three chemical agents, namely, ethanol, pyrethroid, and hydrogen peroxide. This was achieved through a two-step process. The first step was experimentally achieved by in situ recording of the changes to the extracellular electrical activity from the sensing sites or the array of microelectrodes that form the platform for patterning neurons. Simultaneous optical characterization of the cell array during the sensing process was performed to identify the associated physiological changes. The second step was mathematical and was based on developing a library of signature patterns for a set of concentrations of the various combinations of the three chemical agents. Two variants of the nearest neighbor algorithm scheme - (a) partial distance search method, and (b) search tree method, were implemented for the accurate detection of all the components with varying concentrations in the test samples of unknown nature. This technique exhibits reliability in identification up to parts-per-billion (ppb) sensitivity. The capability of standardization of this technique for potential commercial applications is also discussed.

Highly sensitive and selective amperometric microbial biosensor for direct determination of p-nitrophenyl-substituted organophosphate nerve agents

We report herein a whole cell-based amperometric biosensor for highly selective, highly sensitive, direct, single-step, rapid, and cost-effective determination of organophosphate pesticides with a p-nitrophenyl substituent. The biosensor was comprised of a p-nitrophenol degrader, Pseudomonas putida JS444, genetically engineered to express organophosphorus hydrolase (OPH) on the cell surface immobilized on the carbon paste electrode. Surface-expressed OPH catalyzed hydrolysis of the p-nitrophenyl substituent organophosphorus pesticides such as paraoxon, parathion, and methyl parathion to release p-nitrophenol, which was subsequently degraded by the enzymatic machinery of P. putida JS444. The electrooxidization current of the intermediates was measured and correlated to the concentration of organophosphates. The best sensitivity and response time were obtained using a sensor constructed with 0.086 mg dry weight of cells operating at 600 mV applied potential (vs Ag/AgCl reference) in 50 mM citrate--phosphate pH 7.5 buffer with 50 microM CoCl2 at room temperature. Under optimum operating conditions the biosensor measured as low as 0.28 ppb of paraoxon, 0.26 ppb of methyl parathion, and 0.29 ppb parathion. These detection limits are comparable to cholinesterase inhibition-based biosensors. Unlike the inhibition-based format, this biosensor manifests a selective response to organophosphate pesticides with a p-nitrophenyl substituent only, has a simplified single-step protocol with short response time, and can be used for repetitive/multiple and on-line analysis. The service life of the microbial amperometric biosensor was 5 days when stored in the operating buffer at 4 degrees C. The new biosensor offers great promise for rapid environmental monitoring of OP pesticides with nitrophenyl substituent.

Affinity adsorbent based on combinatorial phage display peptides that bind alpha-cobratoxin

Combinatorial phage display was used to discover peptides that selectively bind to the alpha-cobratoxin (neurotoxin) component of the multi-component venom of the Thai cobra, Naja kaouthia. Peptide sequences determined in this way were synthesized chemically and were covalently attached to agarose through the alpha-amino terminus. Such affinity chromatography supports selectively bound the alpha-cobratoxin component from crude venom, while passage of the crude venom over the support selectively depleted the venom of this component. The selective binding of alpha-cobratoxin to peptide-based solid-phase supports suggests that a limitless variety of peptides similarly obtained by combinatorial phage display can be used to craft specific analytical and preparative tools.

Dielectrophoretic traps for single-particle patterning

We present a novel microfabricated dielectrophoretic trap designed to pattern large arrays of single cells. Because flowing away untrapped cells is often the rate-limiting step during cell patterning, we designed the trap to be strong enough to hold particles against practical flow rates. We experimentally validated the trap strength by measuring the maximum flow rate that polystyrene beads could withstand while remaining trapped. These bead experiments have shown excellent agreement with our model predictions, without the use of fitting parameters. The model was able to provide us with a fundamental understanding of how the traps work, and additionally allowed us to establish a set of design rules for optimizing the traps for a wide range of cell sizes. We provide the foundations for an enabling technology that can be used to pattern cells in unique ways, allowing us to do novel cell biology experiments at the microscale.

Neuron-based microarray sensors for environmental sensing

We present a novel sensing scheme for detecting the effects of unburned fossil fuels by integrating microarray technology and dielectrophoresis to develop single-neuron arrays. These arrays have the capability to sense and identify the two fuels, at parts per billion (ppb) concentrations, as well to determine the associated physiological changes at the single-cell level. Identification is achieved through frequency domain analysis of the measured changes to the extracellular electrical activity due to the effect of the fossil fuels. This yields unique electrical identifiers known as "signature patterns". Simultaneous optical visualization to the physiological changes is obtained by specific fluorescent staining. The correlation between the signature patterns and the cellular biological behavior establishes the veracity of this identification technique.

Whole cell-enzyme hybrid amperometric biosensor for direct determination of organophosphorous nerve agents with p-nitrophenyl substituent

In this paper, we reported the construction of a hybrid biosensor for direct, highly selective, sensitive, and rapid quantitative determination of organophosphate pesticides with p-nitrophenyl substituent using purified organophosphorus hydrolase (OPH) for the initial hydrolysis and Arthrobacter sp. JS443 for subsequent p-nitrophenol oxidation. The biocatalytic layer was prepared by co-immobilizing Arthrobacter sp. JS443 and OPH on a carbon paste electrode. OPH catalyzed the hydrolysis of organophosphorus pesticides with p-nitrophenyl substituent such as paraoxon and methyl parathion to release p-nitrophenol that was oxidized by the enzymatic machinery of Arthrobacter sp. JS443 to carbon dioxide through electroactive intermediates 4-nitrocatechol and 1,2,4-benzenetriol. The oxidization current of the intermediates was measured and correlated to the concentration of organophosphates. The best sensitivity and response time were obtained using a sensor constructed with 0.06 mg dry weight of cell and 965 IU of OPH operating at 400 mV applied potential (vs. Ag/AgCl reference) in 50 mM citrate-phosphate pH 7.5 buffer at room temperature. Using these conditions, the biosensor measured as low as 2.8 ppb (10 nM) of paraoxon and 5.3 ppb (20 nM) of methyl parathion without interference from phenolic compounds, carbamate pesticides, triazine herbicides, and organophosphate pesticides that do not have the p-nitrophenyl substituent. The biosensor had excellent operational life-time stability with no decrease in response for more than 40 repeated uses over a 12-h period when stored at room temperature, while its storage life was approximately 2 days when stored in the operating buffer at 4 degrees C.

Detection and classi?cation of threat agents via high-content assays of mammalian cells

One property common to all chemical or biological threat agents is that they damage mammalian cells. A threat detection and classification method based on the effects of compounds on cells has been developed. This method employs high-content screening (HCS), a concept in drug discovery that enables those who practice cell-based assays to generate deeper biological information about the compounds they are testing. A commercial image-based cell screening platform comprising fluorescent reagents, automated image acquisition hardware, image analysis algorithms, data management and informatics was used to develop assays and detection/classification methods for threat agents. These assays measure a cell's response to a compound, which may include activation or inhibition of signal transduction pathways, morphological changes or cytotoxic effects. Data on cell responses to a library of compounds was collected and used as a training set. At the EILATox-Oregon Workshop, cellular responses following exposure to unknown samples were measured by conducting assays of p38 MAP kinase, NF-kappaB, extracellular-signal related kinase (ERK) MAP kinase, cyclic AMP-response element binding protein (CREB), cell permeability, lysosomal mass and nuclear morphology. Although the assays appeared to perform well, only four of the nine toxic samples were detected. However the system was specific, because no false positives were detected. Opportunities for improvement to the system were identified during the course of this enlightening workshop. Some of these improvements were applied in subsequent tests in the Cellomics laboratories, resulting in a higher level of detection. Thus, an HCS approach was shown to have potential in detecting threat agents, but additional work is necessary to make this a comprehensive detection and classification system.

Neurons as sensors: individual and cascaded chemical sensing

A single neuron sensor has been developed based on the interaction of gradient electric fields and the cell membrane. Single neurons are rapidly positioned over individual microelectrodes using positive dielectrophoretic traps. This enables the continuous extracellular electrophysiological measurements from individual neurons. The sensor developed using this technique provides the first experimental method for determining single cell sensitivity; the speed of response and the associated physiological changes to a broad spectrum of chemical agents. Binding of specific chemical agents to a specific combination of receptors induces changes to the extracellular membrane potential of a single neuron, which can be translated into unique "signature patterns" (SP), which function as identification tags. Signature patterns are derived using Fast Fourier Transformation (FFT) analysis and Wavelet Transformation (WT) analysis of the modified extracellular action potential. The validity and the sensitivity of the system are demonstrated for a variety of chemical agents ranging from behavior altering chemicals (ethanol), environmentally hazardous agents (hydrogen peroxide, EDTA) to physiologically harmful agents (pyrethroids) at pico- and femto-molar concentrations. The ability of a single neuron to selectively identify specific chemical agents when injected in a serial manner is demonstrated in "cascaded sensing".

Biomaterials for mediation of chemical and biological warfare agents

Recent events have emphasized the threat from chemical and biological warfare agents. Within the efforts to counter this threat, the biocatalytic destruction and sensing of chemical and biological weapons has become an important area of focus. The specificity and high catalytic rates of biological catalysts make them appropriate for decommissioning nerve agent stockpiles, counteracting nerve agent attacks, and remediation of organophosphate spills. A number of materials have been prepared containing enzymes for the destruction of and protection against organophosphate nerve agents and biological warfare agents. This review discusses the major chemical and biological warfare agents, decontamination methods, and biomaterials that have potential for the preparation of decontamination wipes, gas filters, column packings, protective wear, and self-decontaminating paints and coatings.

Detection of frequency resonance energy transfer pair on double-labeled microsphere and Bacillus anthracis spores by flow cytometry

Development of an ultrasensitive biosensor for biological hazards in the environment is a major need for pollutant control and for the detection of biological warfare. Fluorescence methods combined with immunodiagnostic methods are the most common. To minimize background noise, arising from the unspecific adsorption effect, we have adapted the FRET (frequency resonance energy transfer) effect to the immunofluorescence method. FRET will increase the selectivity of the diagnosis process by introducing a requirement for two different reporter molecules that have to label the antigen surface at a distance that will enable FRET. Utilizing the multiparameter capability of flow cytometry analysis to analyze the double-labeling/FRET immunostaining will lead to a highly selective and sensitive diagnostic method. This work examined the FRET interaction of fluorescence-labeled avidin molecules on biotin-coated microspheres as a model system. As target system, we have used labeled polyclonal antibodies on Bacillus anthracis spores. The antibodies used were purified immunoglobulin G (IgG) molecules raised in rabbits against B. anthracis exosoporium components. The antibodies were fluorescence labeled by a donor-acceptor chromophore pair, alexa488 as a donor and alexa594 as an acceptor. On labeling the spores with alexa488-IgG as a donor and alexa594-IgG as an acceptor, excitation at 488 nm results in quenching of the alexa-488 fluorescence (E(q) = 35%) and appearance of the alexa594 fluorescence (E(s) = 22%), as detected by flow cytometry analysis. The FRET effect leads to a further isolated gate (FL1/FL3) for the target spores compared to competitive spores such as B. thuringiensis subsp. israelensis and B. subtilis. This new approach, combining FRET labeling and flow cytometry analysis, improved the selectivity of the B. anthracis spores by a factor of 10 with respect to B. thuringiensis subsp. israelensis and a factor of 100 with respect to B. subtilis as control spores.

A microfluidic bioreactor based on hydrogel-entrapped E. coli: cell viability, lysis, and intracellular enzyme reactions

Viable E. coli cells were entrapped in hydrogel micropatches photopolymerized within microfluidic systems. The microfluidic channels and the micropatches have sizes on the order of 100-500 microm. Small molecules, such as dyes and surfactants, present in the solution surrounding the hydrogel, are able to diffuse into the gel and encounter the cells, but the cells are sufficiently large to be retained. For example, sodium dodecyl sulfate is a lysis agent that is able to penetrate the hydrogel and disrupt the cellular membrane. Entrapment of viable cells within hydrogels, followed by lysis, could provide a convenient means for preparing biocatalysts without the need for enzyme extraction and purification. Hydrogel-immobilized cells are able to carry out chemical reactions within microfluidic channels. Specifically, a nonfluorescent dye, BCECF-AM, is able to penetrate both the hydrogel and the bacterial membrane and be converted into a fluorescent form (BCECF) by the interior cellular machinery. These results suggest that cells immobilized within microfluidic channels can act as sensors for small molecules and as bioreactors for carrying out reactions.

Application of natural receptors in sensors and assays

Biosensors are analytical devices that use a biological or biologically derived material immobilized at a physicochemical transducer to measure one or more analytes. Although there are a large number of reviews on biosensors in general, there has been little systematic information presented on the application of natural receptors in sensor technology. This perspective discusses broadly the fundamental properties of natural receptors, which make them an attractive option for use as biorecognition elements in sensor technology. It analyses the current situation by reference to typical examples, such as the application of nicotinic acetylcholine receptor and G protein-linked receptors in affinity sensors and analyses the problems that need to be resolved prior to any commercialization of such devices.

Detection of Staphylococcus aureus enterotoxin B at femtomolar levels with a miniature integrated two-channel surface plasmon resonance (SPR) sensor

Surface plasmon resonance (SPR) biosensors offer the capability for continuous real-time monitoring. The commercial instruments available have been large in size, expensive, and not amenable to field applications. We report here an SPR sensor system based on a prototype two-channel system similar to the single channel Spreeta devices. This system is an ideal candidate for field use. The two-channel design provides a reference channel to compensate for bulk refractive index (RI), non-specific binding and temperature variations. The SPR software includes a calibration function that normalizes the response from both channels, thus enabling accurate referencing. In addition, a temperature-controlled enclosure utilizing a thermo-electric module based on the Peltier effect provides the temperature stability necessary for accurate measurements of RI. The complete SPR sensor system can be powered by a 12V battery. Pre-functionalized, disposable, gold-coated thin glass slides provide easily renewable sensor elements for the system. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detectable at sub-nanomolar levels and with amplification at femtomolar levels. A regeneration procedure for the sensor surface allowed for over 60 direct detection cycles in a 1-month period.

Biosensor technologies for detecting microbiological foodborne hazards

The convergence of molecular biology and miniaturized instrumentation has accelerated development of biosensors with the specifications necessary to support pathogen reduction and quality programs in the food supply. Advances in optoelectronics, thin layer deposition, and microfabrication have provided many options for achieving microbiological detection goals. Some promising technologies are reviewed.

Biomolecular recognition on well-characterized beads packed in microfluidic channels

We describe a new approach for the analysis of biomolecular recognition in microfluidic channels. The method involves real-time detection of soluble molecules binding to receptor-bearing microspheres, sequestered in affinity column format inside a microfluidic channel. Identification and quantitation of analytes occurs via direct fluorescence measurements or fluorescence resonance energy transfer (FRET). We establish a model system that detects the FLAG epitope. The assay can potentially detect subfemtomole quantities of antibody with a high signal-to-noise ratio and a large dynamic range spanning nearly 4 orders of magnitude in analyte concentration in microliter-to-submicroliter volumes of analyte fluid. Kinetic and equilibrium constants for the reaction of this receptor-ligand pair are obtained through modeling of kinetic responses of the affinity microcolumn and are consistent with those obtained by flow cytometry. Because of the correlation between kinetic and equilibrium data obtained for the microcolumns, quantitative analysis can be done prior to the steady-state end point of the recognition reaction. This method has the promise of combining the utility of affinity chromatography with the advantage of direct, quantitative, and real-time analysis and the cost-effectiveness of microanalytical devices. The approach has the potential to be generalized to a host of bioaffinity assay methods including analysis of protein complexes and molecular assembly and microsystem-based multianalyte determinations.

Detection of physiologically active compounds using cell-based biosensors

Cell-based biosensors are portable devices that contain living biological cells that monitor physiological changes induced by exposure to environmental perturbations such as toxicants, pathogens or other agents. Methods of detecting physiological changes include extracellular electrical recordings, optical measurements, and, in the future, functional genomics and proteomics. Several technical developments are occurring that will increase the feasibility of cell-based biosensors for field applications; these developments include stem cell and 3D culture technologies. Possible scenarios for the use of cell-based biosensors include broad-range detectors of unknown threat agents and functional assessment of identified agents.

Flow injection amperometric enzyme biosensor for direct determination of organophosphate nerve agents

A flow injection amperometric biosensor for the determination of organophosphate nerve agents was developed. The biosensor incorporated an immobilized enzyme reactor that contains the enzyme organophosphorus hydrolase covalently immobilized on activated aminopropyl controlled pore glass beads and an electrochemical flow-through detector containing carbon paste working electrode, a silver/silver chloride reference electrode, and stainless steel counter electrode. The organophosphorus hydrolase catalyzed the hydrolysis of organophosphate with nitrophenyl substituent to generate p-nitrophenol which is then detected downstream electrochemically at the carbon paste electrode poised at 0.9 V vs the reference electrode. The amperometric response of the biosensor was linear up to 120 microM and 140 microM, with lower detection limits of 20 nM and 20 nM, for paraoxon and methyl parathion, respectively. The response was very reproducible (RSD 2%, n = 35) and stable for over 1 month when the immobilized enzyme column was stored at 4 degrees C. Each assay took ca. 2 min giving a sample throughput of 30 h(-1). The applicability of the biosensor to monitor paraoxon and methyl parathion in distilled water and simulated well water was demonstrated.

Optical sensors for detection of bacteria. 1. General concepts and initial development

The concept of using immobilized nucleic acid stains as detection chemistry to fabricate optical bacterial sensors is first demonstrated. SYTO 13 (a green fluorescent cell stain) is used as the molecular recognition element and fluorescent reporter in the sensor. The sensor responds to aqueous and aerosolized bacterial samples in 15 and 30 min, respectively. In addition, the sensor can discriminate a change in Pseudomonas aeruginosa (Pa) cell concentration of 1 order of magnitude or less and can detect down to 2.4 x 10(5) cells/mL of Pa cells. The utility of the sensor is demonstrated by monitoring the growth of a Pa cell culture over a period of 50 h.

The Role of the Clinical Laboratory in Managing Chemical or Biological Terrorism

Background: Domestic and international acts of terrorism using chemicals and pathogens as weapons have recently attracted much attention because of several hoaxes and real incidents. Clinical laboratories, especially those affiliated with major trauma centers, should be prepared to respond rapidly by providing diagnostic tests for the detection and identification of specific agents, so that specific therapy and victim management can be initiated in a timely manner. As first-line responders, clinical laboratory personnel should become familiar with the various chemical or biological agents and be active participants in their local defense programs.

Approach: We review the selected agents previously considered or used in chemical and biological warfare, outline their poisonous and pathogenic effects, describe techniques used in their identification, address some of the logistical and technical difficulties in maintaining such tests in clinical laboratories, and comment on some of the analytical issues, such as specimen handling and personal protective equipment.

Content: The chemical agents discussed include nerve, blistering, and pulmonary agents and cyanides. Biological agents, including anthrax and smallpox, are also discussed as examples for organisms with potential use in bioterrorism. Available therapies for each agent are outlined to assist clinical laboratory personnel in making intelligent decisions regarding implementation of diagnostic tests as a part of a comprehensive defense program.

Summary: As the civilian medical community prepares for biological and chemical terrorist attacks, improvement in the capabilities of clinical laboratories is essential in supporting counterterrorism programs designed to respond to such attacks. Accurate assessment of resources in clinical laboratories is important because it will provide local authorities with an alternative resource for immediate diagnostic analysis. It is, therefore, recommended that clinical laboratories identify their current resources and the extent of support they can provide, and inform the authorities of their state of readiness.

New technologies in medicine: biotechnology and nanotechnology

In February 1997, researchers created Dolly, a lamb cloned from the DNA of an adult sheep. This was supposed to be impossible (or at least generations away), but suddenly it was here--a clone of a higher mammal. Whatever Dolly's ultimate significance, she conclusively demonstrated the growing power of biotechnology. Many have come to the conclusion that advances in biotechnology will fundamentally transform medicine during the coming decade. Society is in the midst of a technical revolution that will have the same relevance as the development of the printing press, the internal combustion engine, and the microprocessor. Computers have become the key tools in the accelerating progress that is occurring in the field of biotechnology. At the same time, genetic, evolutionary, and other biologic processes are providing new models for the development of computer hardware and software. Today represents the early stages of what has been called the "bionic convergence": the convergence of the biologic revolution with the information revolution, the joining of biology with electronics. Virtually everything that is important to health care practitioners and patients--diagnostic techniques, means of understanding disease causes, methods of treatment, approaches to prevention, health care facility design, medical education, and legal and ethical issues--will be changed by the revolutions currently underway in the fields of biotechnology and genetic medicine. The following monograph includes several forecasts about a range of possible opportunities that may have enormous effects on health care during the next century. These forecasts address the potential impacts of biotechnology on disease detection and diagnosis, treatment, prevention, nanotechnology, and other areas of medical significance. Every area of beneficiary care will be affected as the changes implied by these forecasts begin to develop. Beneficiary care will continue to see the emergence of a "forecast, prevent, and manage" paradigm. The emphasis will be on disease prevention, health promotion, and the creation of healthy communities. New diagnostic and treatment opportunities will be available as a consequence of breakthroughs in genetic medicine. The health care system will view health as a whole, as a person's overall sense of well-being--an entity that encompasses much more than the absence of symptoms.

Utilization of enzyme-substrate interactions in analytical chemistry

Enzymes are capable of a highly specific interaction with a variety of substances including their respective substrates. This review summarizes how such interactions may be used in analytical (bio-)chemistry, e.g., for the elucidation of the binding mechanism, the determination of the binding strength, the carting of the binding site, or the screening of possible substrate/inhibitor molecules. Possible assay formats such as analytical affinity chromatography, affinity capillary electrophoresis (ACE), conventional affinity gel electrophoresis (AEP), and related techniques are discussed together with examples of recent applications. In addition a brief section on enzyme-substrate reactions as tools in analytical chemistry is included, since these are perhaps even more important to analytical (bio-)chemistry. The development and application of bioanalytical systems and especially biosensors in various fields including medicine, biotechnology, agriculture, defense and foodstuffs are considered.

Biosensor for direct determination of organophosphate nerve agents. 1. Potentiometric enzyme electrode

A potentiometric enzyme electrode for the direct measurement of organophosphate (OP) nerve agents was developed. The basic element of this enzyme electrode was a pH electrode modified with an immobilized organophosphorus hydrolase (OPH) layer formed by cross-linking OPH with bovine serum albumin (BSA) and glutaradehyde. OPH catalyses the hydrolysis of organophosphorus pesticides to release protons, the concentration of which is proportional to the amount of hydrolysed substrate. The sensor signal and response time was optimized with respect to the buffer pH, ionic concentration of buffer, temperature, and units of OPH immobilized using paraoxon as substrate. The best sensitivity and response time were obtained using a sensor constructed with 500 IU of OPH and operating in pH 8.5, 1 mM HEPES buffer. Using these conditions, the biosensor was used to measure as low as 2 microM of paraoxon, ethyl parathion, methyl parathion and diazinon. The biosensor was completely stable for at least one month when stored in pH 8.5, 1 mM HEPES + 100 mM NaCl buffer at 4 degrees C.

An analysis of analyte-receptor binding kinetics for biosensor applications: influence of the fractal dimension on the binding rate coefficient

The diffusion-limited binding kinetics of analyte in solution to receptor immobilized on a biosensor surface is analysed within a fractal framework. Both a single- as well as a dual-fractal analysis are utilized. Antigen-antibody and analyte-receptor systems are analysed. For the antigen-antibody and analyte-receptor systems where a single- or a dual-fractal analysis was used, it is of interest to note that the binding rate coefficient and the fractal dimension exhibit changes in the same direction. The binding rate coefficient expressions obtained as a function of the fractal dimension indicate the high sensitivity of the binding rate coefficient with respect to the fractal dimension. For example, for a single-fractal analysis and for the binding of (a) 1 microM BSA in solution to the anti-BSA-protein fused to a biosensor surface, and for (b) the binding of m-xylene-saturated STE buffer solution to the microorganism immobilized to the fiber-optic end and covered with a polycarbonate membrane, the orders of dependence of the binding rate coefficient on the fractal dimension were 5.535 and 3.314, respectively. This emphasizes the importance of the degree of heterogeneity on the biosensor surface and its impact on the binding rate coefficient, k. This high sensitivity is also indicated for a dual-fractal analysis, at least for the binding rate coefficient, k2. For example, during regeneration runs and for the binding of polymerase chain-reaction amplified DNA in solution to DNA capture protein immobilized on a fiber-optic biosensor, the order of dependence of k2 on Df2 was 3.399. The fractional order of dependence of the binding rate coefficient(s) on the fractal dimension(s) further reinforces the fractal nature of the system. The binding rate coefficient expressions developed as a function of the fractal dimension for both single-fractal analysis and dual-fractal analysis systems are of particular value since they provide a means to better control biosensor performance by linking it to the heterogeneity on the surface. Also, the importance of the nature of the surface on biosensor performance is emphasized in a quantitative sense.